design-systems: add 74 brand DESIGN.md files (VoltAgent/awesome-design-md)

- 74 brands: airbnb, stripe, apple, figma, linear, vercel, etc.
- 147 files: DESIGN.md + README.md per brand (~2.1 MB)
- Each DESIGN.md contains structured brand analysis (colors, typography, components)
- Updated 00-overview.md with new design-systems directory

concepts/accessibility-standards.md

@@ -0,0 +1,63 @@
+---
+title: Accessibility (WCAG) Standards
+description: Web accessibility guidelines for premium design.
+tags: [accessibility, wcag, contrast, screen-reader, keyboard]
+---
+
+# Accessibility (WCAG) Standards
+
+## WCAG 2.1 Level AA Requirements
+
+### 1. Perceivable
+- Text alternatives for non-text content
+- Captions for multimedia
+- Content adaptable (1 column, no scroll)
+- Color contrast: 4.5:1 (normal), 3:1 (large)
+
+### 2. Operable
+- Keyboard accessible
+- Enough time to read/use
+- No flashing >3 times/second
+- Navigable (skip links, headings, focus)
+
+### 3. Understandable
+- Readable text
+- Predictable navigation
+- Input assistance (labels, placeholders)
+
+### 4. Robust
+- Compatible with assistive tech
+- Valid HTML
+- ARIA labels where needed
+
+## Focus Management
+
+```css
+:focus-visible {
+  outline: 2px solid var(--accent-primary);
+  outline-offset: 2px;
+  border-radius: 2px;
+}
+```
+
+## Screen Reader Patterns
+
+```html
+<!-- Skip link -->
+<a href="#main" class="skip-link">Skip to content</a>
+
+<!-- Landmarks -->
+<header role="banner">...</header>
+<nav role="navigation">...</nav>
+<main role="main">...</main>
+<footer role="contentinfo">...</footer>
+
+<!-- Live regions -->
+<div aria-live="polite" role="status">Loading...</div>
+```
+
+## Anti-Patterns
+- Never rely on color alone
+- Never remove focus outlines without replacement
+- Never use `display: none` for hiding content that should be accessible
+- Never skip heading hierarchy (h1 → h2 → h3)